This invention relates generally to an internal combustion engine and more particularly to operation of engine valves to facilitate engine braking or compression braking.
Compression brakes are well know devices in the industry used to provide additional stopping force especially in large vehicles. In a standard four-cycle operation during a combustion stroke, an exhaust valve is generally in a closed position from near bottom dead center (BDC) to top dead center (TDC) and back to BDC. During a compression brake operation during the combustion stroke, the exhaust valve generally opens as a piston moves from BDC to TDC and closes as the piston moves from TDC to BDC.
One manner of controlling operation of the exhaust valve during a brake operation involves using a master piston and a slave piston. As shown in U.S. Pat. No. 4,150,640 issued to Egan on Apr. 24, 1979, the master piston operates in response to movement of a fuel injection cam. Fixing brake actuation to the fuel injection cam may tend to maintain the exhaust valve open for an extended period after the piston reaches TDC.
Other systems have added more complicated actuation mechanisms to provide control with less ties to a fixed cam lobe. U.S. Pat. No. 5,526,784 issued to Hakkenbert et al on Jun. 18, 1996 uses electronically controlled hydraulic actuation to control operation of the exhaust valve. These systems provide greater control over brake actuation. Cost and complexity may prevent implementation of these systems in some applications.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a compression brake system for an internal combustion engine has a master cylinder and a master piston slidably positioned therein. A brake actuator cylinder connects with the master cylinder. A brake actuator piston positioned in the brake actuator cylinder actuates a valve. In a first position, the brake actuator piston limits fluid communication between the master cylinder and a second actuator volume. In a second position, the brake actuator piston allows fluid communication between the master cylinder and the second actuator volume.